Entry of a sub state does only call the entry action of the sub state, but not of the initial state of the sub state.

Describe the bug
MSVC fails to compile if constexpr branches even if the condition for the branch does not evaluate to true.

This is needed to sm.h:

  if constexpr (has_anonymous_transition(rootState)) {
  ...
  auto& result = get_dispatch_table_entry(event, region);
  ...
  }

To Reproduce
Compiles on clang: https://godbolt.org/z/e3KcYv
Does not compile on msvc: https://godbolt.org/z/ab3bdPj91

Expected behavior
Compiles.

Additional context
A workaround could be to add some kind of a dummy next state for the none event.

Problem:
The hsm does not provide a function to compose multiple actions into a single one.

Solution:
Provide a function and operator for the dsl e.g.:

hsm::state<S1> {}          + hsm::event<e1> {} / (log, update) = hsm::state<S2> {}, // log and update get composed
hsm::state<S1> {}          + hsm::event<e1> {} / compose(log, update) = hsm::state<S2> {}, // log and update get composed

Hi,
Describe the bug
The on_exit is never called for the initial state neither in the main state nor a substate. But the on_entry is sometimes call.

To Reproduce

    #include <hsm/hsm.h>
    
    #include <iostream>
    
    #define ON_ENTRY(STATE)                                                                                                                   \
        static constexpr auto on_entry()                                                                                                      \
        {                                                                                                                                     \
            return [](const auto& event, const auto& source, const auto& target) { std::cout << "      -- ENTRY: " << #STATE << std::endl; }; \
        }
    
    #define ON_EXIT(STATE)                                                                                                                   \
        static constexpr auto on_exit()                                                                                                      \
        {                                                                                                                                    \
            return [](const auto& event, const auto& source, const auto& target) { std::cout << "      -- EXIT: " << #STATE << std::endl; }; \
        }
    
    #define ON(STATE)   \
        ON_ENTRY(STATE) \
        ON_EXIT(STATE)
    
    namespace ee {
    struct Idle {
        ON(Idle);
    };
    
    struct A0 {
        ON(A0);
    };
    // --------------------------------------------------------------------------
    // States
    struct A1 {
        ON(A1);
    };
    
    struct A2 {
        ON(A2);
    };
    
    // --------------------------------------------------------------------------
    // Events
    struct press {};
    struct start {};
    struct stop {};
    
    // --------------------------------------------------------------------------
    // Guard
    const auto success = [](auto /*event*/, auto /*source*/, auto /*target*/) { return true; };
    
    // --------------------------------------------------------------------------
    // Actions
    const auto log = [](auto event, auto source, auto target, const char* msg = "") {
        std::cout << msg << typeid(source).name() << " + " << typeid(event).name() << " = " << typeid(target).name() << std::endl;
    };
    
    // --------------------------------------------------------------------------
    // State machines
    struct SubState {
        static constexpr auto make_transition_table()
        {
            // clang-format off
                return hsm::transition_table(
                    // Source              + Event            [Guard]   / Action  = Target
                    // +-------------------+------------------+---------+---------+----------------------+
                    * hsm::state<A0>       + hsm::event<press>          / log     = hsm::state<A1>,
                      hsm::state<A1>       + hsm::event<press>          / log     = hsm::state<A2>,
                      hsm::state<A2>       + hsm::event<press>          / log     = hsm::state<A0>
                    );
    
            // clang-format on
        }
    
        ON(SubState);
    
        static constexpr auto on_unexpected_event()
        {
            return [](auto& event, const auto& state) { log(event, state, state, "unexpected event: "); };
        }
    };
    
    struct Initial {
    
        static constexpr auto make_transition_table()
        {
            // clang-format off
                return hsm::transition_table(
                    // Source              + Event            [Guard]   / Action  = Target
                    // +-------------------+------------------+---------+---------+----------------------+
                    * hsm::state<Idle>       + hsm::event<start>          / log     = hsm::state<SubState>,
                      hsm::state<SubState>   + hsm::event<stop>           / log     = hsm::state<Idle>
                    );
    
            // clang-format on
        }
    
        ON(Initial);
    
        static constexpr auto on_unexpected_event()
        {
            return [](auto& event, const auto& state) { log(event, state, state, "unexpected event: "); };
        }
    };
    
    }   // namespace ee
    
    int main()
    {
        std::cout << "------------------------------------------- Initial" << std::endl;
        {
            hsm::sm<ee::Initial> fsm;
    
            fsm.process_event(ee::start{});
    
            for (int i = 0; i < 4; ++i) {
                std::cout << "----- process_event(press) ----- " << std::endl;
                fsm.process_event(ee::press{});
            }
    
            fsm.process_event(ee::stop{});
        }
    
        std::cout << "------------------------------------------- SubState" << std::endl;
        {
            hsm::sm<ee::SubState> fsm;
    
            for (int i = 0; i < 4; ++i) {
                std::cout << "----- process_event(press) ----- " << std::endl;
                fsm.process_event(ee::press{});
            }
        }
    }

Expected behavior
On_exit called every time a state is exited (at least when the on_entry was called)

Additional context

output:

------------------------------------------- Initial (with a substate)
struct ee::Idle + struct ee::start = struct ee::A0
-- ENTRY: SubState
-- ENTRY: A0
----- process_event(press) -----
here expecting EXIT: A0

struct ee::A0 + struct ee::press = struct ee::A1
-- ENTRY: A1
----- process_event(press) -----
-- EXIT: A1
struct ee::A1 + struct ee::press = struct ee::A2
-- ENTRY: A2
----- process_event(press) -----
-- EXIT: A2
struct ee::A2 + struct ee::press = struct ee::A0
-- ENTRY: A0
----- process_event(press) -----

here expecting EXIT: A0

struct ee::A0 + struct ee::press = struct ee::A1
-- ENTRY: A1
-- EXIT: SubState
<- here the sate on_exit is called which is great
struct ee::SubState + struct ee::stop = struct ee::Idle
-- ENTRY: Idle
<- here ENTRY is called but was not called at the start, nor the EXIT is called

------------------------------------------- SubState
----- process_event(press) -----
here, may be EXIT expected, may by ENTRY too for A0
struct ee::A0 + struct ee::press = struct ee::A1
-- ENTRY: A1
----- process_event(press) -----
-- EXIT: A1
struct ee::A1 + struct ee::press = struct ee::A2
-- ENTRY: A2
----- process_event(press) -----
-- EXIT: A2
struct ee::A2 + struct ee::press = struct ee::A0
-- ENTRY: A0
----- process_event(press) -----
here ENTRY: A0 was called, but not EXIT
struct ee::A0 + struct ee::press = struct ee::A1
-- ENTRY: A1

Unfortunately, the code itself is beeyond my template/boost.Hana knowledge, If I have some tips to find the issue or change the behavior, may be I can help.

Regards,

Found a howto here https://medium.com/rkttu/write-your-github-actions-workflow-for-build-windows-application-94e5a989f477

Current list notation:
hsm::transition(src_state, event, guard, action, dst_state)
In pre fix notation:
dst_state <= src_state + event [ guard ] / action

Problem:
a transition into a substate like the following does not call the substates entry action

  * hsm::state<S1>{} + hsm::event<enterSubState>{}   = hsm::state<SubState>{}

Workaround:
it does work when you provide a dummy action:

  * hsm::state<S1>{} + hsm::event<enterSubState>{}   / dummy = hsm::state<SubState>{}

...so the following use case can be supported (https://cppx.godbolt.org/z/YdxpJ6):

#include <memory>
#include <string>
#include <iostream>

struct MyDependency {
    std::string data = "42";
};

template <class Dependency>
struct StateMachine {
    StateMachine(Dependency& dependency) : dependency(dependency)
    {        
    }

    Dependency& dependency;
};


struct A {
    A() : 
      dep(MyDependency{}), 
      sm(StateMachine<MyDependency>{dep}){
        
    }

    A(A&& other) : 
        dep(std::move(other.dep)),
        sm(std::move(other.sm))
    {
        sm.dependency = dep;
    }

    MyDependency dep;
    StateMachine<MyDependency> sm;

};

int main() {
    A a;
    
    std::cout << "before move:" << std::endl;
    std::cout << "dep: " << a.dep.data << std::endl;
    std::cout << "ref: " << a.sm.dependency.data << std::endl;

    auto b = std::move(a);

    std::cout << "after move:" << std::endl;
    std::cout << "dep: " << b.dep.data << std::endl; 
    std::cout << "ref: " << b.sm.dependency.data << std::endl;

}

Such as:
hsm::state<S1>{} = hsm::state<S2>{}
hsm::state<S1>{} / action = hsm::state<S2>{}
hsm::state<S1>{} [guard] / action = hsm::state<S2>{}

The install target does not need to build tests and benchmarks.

Found howto here https://rhonabwy.com/2020/05/09/continuous-integration-with-github-actions-for-macos-and-ios-projects/

• Boost version
• Compiler versions
• C++ version

Problem

In the case you call hsm.process_event(MyEvent{}) with an event type that is not known to the state machine than a complex error is printed by the compiler.

Proposed Solution

Assert statically that the event processed is part of the list of events.

I have a complex state machine (with subs) with several dozen states and transitions. Released on boost::msm.

And I have 2 problems with it:

1. Long compilation time. About 2 minutes for any change of code.
2. The huge amount of memory required by the compiler to compile the given state machine. I saw with my own eyes the consumption of 7 GB of memory at its peak.

I can forgive the lengthy compilation. There are mechanisms that have helped me reduce the need to constantly recompile the state machine.

But the huge amount of memory for the compiler confuses me a lot. This required me to use VS 2022 (in Preview state) and compile a 64-bit application.

I'm in the middle of looking for a finite state machine library with similar functionality to boost::msm, but requiring less memory to compile (less than 4GB).

Please add an approximate comparison of the memory consumed by the compiler when compiling equivalent state machines for the boost::msm and hsm implementations.

Problem
The on_entry action of a state does not get the parent source state as a parameter. But the parent source state could be handy when you need to access its data members e.g. to start a timeout.

Current Workaround
Instead of storing data in the parent source state you can add additional members to the dependency struct.

Proposed Solution

Provide the parent source state to the on_entry function. The same holds true for the parent target state for the on_exit function.

Add some run time benchmark results figure to the readme front page.

The current dispatch table is two dimensional with the indexes current parent state and parents state e.g.: (nextParentState, nextState) = dispatchTable[currentParentState][currentState]

The two level index access could be replaced with a single index access. This would improve performance.

The last state machine benchmark run showed that runtime is very good and on par with sml and msm. Compiletime is on par with msm but a factor 20 higher than sml. Compiletime should be investigated further and the goal is to get onto the same level as sml.

Such as:
hsm::event<e1>
hsm::event<e1> [guard]
hsm::event<e1> / action
hsm::event<e1> [guard] / action

Problem

If you are currently in a sub sub .... sub state of your state machine and an event is triggered triggered in the root state machine then this event is unexpected.

Current Workaround

Don't build state machines with substate level higher then one.

Proposed Solution

When generating substate exits also consider more levels.

Problem

How to run a state activity when I'm on a given state ?

An action is instantaneous: it does not consume time (contrary to the activity). The activity can be seen as a thread that is preempted by any external events the state reacts to. https://cs.emis.de/LNI/Proceedings/Proceedings07/TowardEfficCode_3.pdf

struct MyState {
  MyState(hsm::sm<MyFSM>& fsm)
    : m_sfm(fsm)
   {}

  void tickActivity()
  {
      // do_something not blocking too much
      // Allow m_fsm.process_event(EventXXX {});
  }

  sm::sm<MyFSM>& m_fsm;
};

main()
{
  hsm::sm<MyFSM> fsm;
  while (true)
  {
      fsm.tickActivity(); // Call the current state tickActivity()
      pause(x_ms);
  }
}

The boost msm supports state data members. Which means that your states can have members which you can access on events and actions.

E.g.:

    struct action {
        template <class FSM, class EVT, class SourceState, class TargetState>
        void operator()(EVT const& e, FSM& fsm, SourceState& source, TargetState& target)
        {
           if(target.hasMember){
             std::cout << "this state has a member" << std::endl;
           }
        }
    };

According to https://github.com/google/googletest/blob/master/googletest/README.md, it's best practice to inculde gtest in your project. Currently it's hard to build hsm on MacOS for that reason (homebrew refuses to install googletest globally).

Similiar to here: https://boost-experimental.github.io/sml/examples.html#logging

Actions need to fit onto a particular event e.g.:

const auto action = [](e6 event) {event.called->set_value();};

But it is common that actions are used by different events. In this case, a generalized lambda would be useful:

const auto action = [](auto event) {event.called->set_value();};

The generalized lambda does currently not compile because of the "weird" way actions are called in the library.

Problem:
States need to be default constructable. Thus you can't use a constructor to initialize state data members.

Current workaround:
Initialize a state in its entry action by setting its members or calling an init function

struct Target {
    constexpr auto on_entry()
    {
        return [](auto event, auto source, auto& target) { 
          target.member = std::string("init String"); 
       };
    }
};

Proposed solution by @BenjaminW3:
provide a way to use the constructor of a class and every action call would create a new instance of the target class such as:

const auto action = [](auto&& event, auto source) {
  return Target{std::string("Init string")};
};

or return an instance which is saved externally:

const auto action = [](auto&& event, auto source, auto& dependency) {
  return dependency.target;
}

Problem

The unexpected event handler does currently only get the event as an parameter, but the current state is unknown to the handler. Thats makes it harder to debug in which state the unexpected event was triggered.

Proposed Solution

Provide the current state and parent state to the event handler (at least a string representation of it)

Describe the bug
This segfault appeared when i try to use orthogonal regions with hierarchies.

To Reproduce
https://godbolt.org/z/nzT5MYG91

Expected behavior
I expect this test to pass successfully:

int main()
{
    hsm::sm<MainState> sm;

    sm.process_event(switch_{});
    BOOST_ASSERT(sm.is(0, hsm::state<Online>, hsm::state<S1>));
    BOOST_ASSERT(sm.is(1, hsm::state<Online>, hsm::state<S3>));

    sm.process_event(e1{});
    BOOST_ASSERT(sm.is(0, hsm::state<Online>, hsm::state<S2>));
    BOOST_ASSERT(sm.is(1, hsm::state<Online>, hsm::state<S4>));

    return 0;
}

Additionally, I expect the console output to be:

Region 0!
Region 1!

Additional context
This works good when i remove "Region 1":
https://godbolt.org/z/Kfbe3zean

Record the compile time during ci benchmark compilation of the single benchmark targets.

In multiple files the the namespace is polluted by boost::hana through the alias bh

namespace bh {
using namespace boost::hana;
}

Describe the bug

• The MSVC_RUNTIME_LIBRARY property is only available since CMake 3.15, but I forgot to check this in my PR and the minimum required CMake version in the test CML is 3.14.
• The value of this property is not among the supported set of values.

To Reproduce
-

Expected behavior

• The minimum requirement shouldn't be a lie.
• The value of the property (if this property is even necessary) should be valid.

Additional context
Is this property even necessary?
The VS generator for CMake already uses /MDd for Debug configuration and /MD for everything else.
Is statically linking the CRT for the tests important?

...which is available in conan-center

Such as

hsm::state<S1>{} + hsm::event<e3> {} = hsm::direct<SubState, S1>{}
hsm::direct<SubState, S1>{} + hsm::event<e3> {} = hsm::direct<SubState, S1>{}

As described here : https://www.boost.org/doc/libs/1_72_0/libs/msm/doc/HTML/ch03s02.html#d0e577

Problem
The following transition table shows two transitions which only differ on the guard:

    static constexpr auto make_transition_table()
    {
        // clang-format off
        return hsm::transition_table(
            hsm::state<NotPressed> {} + hsm::event<press> {}                  / blinkOnce  = hsm::state<Pressed> {},
            hsm::state<Pressed> {}    + hsm::event<release> {} [shortPressed] / blinkShort = hsm::state<NotPressed> {},
            hsm::state<Pressed> {}    + hsm::event<release> {} [longPressed]  / blinkLong  = hsm::state<NotPressed> {}
        );
        // clang-format on
    }

Currently, the second transition overwrites the first one.

Current Workaround
You can put some logic in front of the state machine which triggers two different events e.g.: releaseAfterShortPressed and releaseAfterLongPressed

Proposed Solution
One event points to a list of next states in the dispatch table. In the case only a single next state is present performance should not be degraded.

Hi,
when the intial state has a direct transition, it is not activated.

Here the example : entry-exit example

(I try this to have the entry/exit called for my real initial state)

Regards

See disabled test of entry exit action integration test .

The current run time overhead of hsm compared to sml or msm is quite a lot since both sml and msm are deactivating every feature you don't use at compile time. Hsm should also deactivate feature when they are not used. The following list gives an idea of the overhead:

• Call (dummy) action even if no actions are specified ~20% overhead

• Call (dummy) guard even if no guards are specified ~16% overhead

• Check for anonymous transitions even if there are not specified ~16% overhead

• Loop over regions even if there is only one region ~14% overhead

• Check for defers even if no events are deferred ~6% overhead

• Save history even if no history pseudo states are used ~3% overhead

For example a snap: https://ubuntu.com/tutorials/create-your-first-snap#1-overview